The present invention relates to control systems for vehicular drive trains and more particularly vehicles wherein power from a prime mover must be proportioned by the drive train between driven ground wheels of the vehicle and auxillary equipment or implements.
Vehicles employed for earth-moving or material handling operation such as bucket loaders, for example, commonly present the problem of proportioning power from a single prime mover or vehicle engine to the driven ground wheels of the vehicle and also to auxillary equipment or implements such as the bucket on a loader vehicle. It is desirable to provide full power to the vehicle ground wheels during transport operations in order to provide maximum pulling power for the vehicle and to minimize travel time. In other phases of vehicle operation where useful work is being performed by the implements, it is generally desirable to provide maximum power to the implements. However, in many situations, it is necessary to move the vehicle during operation of its implements. Under such circumstances, power from the vehicle engine must be delivered in proper proportion to both the implements and the ground wheels. Slipping clutches and/or torque converters have commonly been employed in the vehicle drive train to perform this proportioning fuction.
An example of such diverse performance requirements for a single vehicle may be readily seen in connection with a bucket loader. In one type of operation, the vehicle may be employed to load material from a stockpile onto a closely adjacent truck. To achieve maximum efficiency, the bucket controls must have full power available to position the bucket as rapidly as possible. In addition, the vehicle itself must move between the stockpile and the truck. In other operations, the loader vehicle may be required to travel extended distances between loading and unloading sites at which time there is a maximum power requirement for its ground wheels.
The speed of operation for the bucket of a loader was initially found to be the limiting factor particularly in a close operating cycle between a stockpile and adjacent truck. Accordingly, it was necessary for the operator to frequently stop the vehicle until the bucket was raised to a sufficient height for dumping its load into the truck. This problem was solved in part by proper selection and sizing of the vehicle engine, its drive train components such as the torque converter and hydraulic circuitry for operating the implement.
Even with such developments, there remains a need to more closely match the vehicle capability with diverse types of operation as described above. One approach to overcoming this problem was the use of torque converters with variable blading providing a proportioning capability of the type discussed above. However, such systems did not commonly provide for full adjustment by the operator. For example, adjustment might be available in low speed ranges of the vehicle. Further, such systems did not generally provide for closely matching the vehicle with widely diverse operating conditions.
Accordingly, there remains a need for control systems to more accurately match the capabilities of a vehicular drive train with operating requirements under widely diverse conditions as discussed above and to improve response of the engine or prime mover. Further, it remains generally desirable to achieve economy both in the size of the vehicle engine, for example, and relative simplicity in the drive train and its control system. It is further desirable to provide such a drive train and control system which minimizes tire slippage since the tire replacement costs for such vehicles are very substantial.